The present invention relates generally to apparatus used in diagnostic imaging and, more particularly, to a method and apparatus for loading and storing radioactive source pins used in combination PET/CT imaging systems.
The combination PET/CT system has been recognized as an effective medical imaging system that can improve patient diagnosis by producing high quality medical images that not only provide anatomical information and images, but also provides physiological information on the patient.
In the combination PET/CT system, radioactive source pins are used to calibrate the PET detector system and to provide attenuation correction during system use or imaging. Because the pins are radioactive, they are stored in a shielded storage device when not in use. The storage device is structurally secure and shields the environment from radiation exposure from the radioactive source pin. Typically, the storage devices and source pins (i.e., source loaders) are generally stored within the PET system, which adds to the overall space requirements for the PET/CT system. The shielded storage device in existing systems is rather large and takes up a considerable amount of space due in part to the fact that the source pin is a rigid member.
During use, the source pin or pins are withdrawn from storage and placed in a rotatable transmission ring within a bore of the PET detector system. The rotatable transmission ring rotates the radioactive source pin about the PET detector system gantry to calibrate the PET detectors. However, because of the large size of the storage device, it is not possible to mount the source pin directly to the rotatable transmission ring. Thus, the storage device and source pin are mounted to the PET system gantry at a location separate from the rotatable transmission ring. When calibration is desired, the source pin is transported to the rotatable transmission ring. This source pin transport time creates potential non-beneficial radiation exposure that should be minimized.
In addition to unwanted radiation exposure, the transport of the source pin from the storage device to the rotation ring also creates a greater opportunity for mechanical or electrical failure to occur in the system. That is, the transition of the radioactive source pin from the storage shield to its mounting on the rotatable transmission ring involves a number of motion steps in which problems can arise. Because the shielding requirements limit the placement of the storage device, the automatic source pin handling and these motion steps are often complex and unreliable.
Therefore, it would be desirable to design a PET/CT system that includes a compact shielded storage device and radioactive source that minimizes storage space requirements within the system. Furthermore, a PET/CT system design that minimizes the probability of mechanical and electrical failure associated with positioning the radioactive source for PET calibration, by eliminating components and motion steps for positioning the radioactive source, is also desired.